linux-kernel - Re: [RFC] [PATCH] A clean approach to writeout throttling

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Message-ID: <25797.1197322312@lwn.net>
Date:	Mon, 10 Dec 2007 14:31:52 -0700
From:	corbet@....net (Jonathan Corbet)
To:	Daniel Phillips <phillips@...nq.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] [PATCH] A clean approach to writeout throttling 

Hey, Daniel,

I'm just getting around to looking at this.  One thing jumped out at me:

> +	if (bio->bi_throttle) {
> +		struct request_queue *q = bio->bi_queue;
> +		bio->bi_throttle = 0; /* or detect multiple endio and err? */
> +		atomic_add(bio->bi_throttle, &q->available);
> +		wake_up(&q->throttle_wait);
> +	}

I'm feeling like I must be really dumb, but...how can that possibly
work?  You're zeroing >bi_throttle before adding it back into
q->available, so the latter will never increase...

jon
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